P414: PATIENT-DERIVED XENOGRAFT MODELS ARE THE LEADING STRATEGY TO IDENTIFY NEW AGENTS FOR PEDIATRIC ACUTE MYELOID LEUKEMIA
Authors: Ambra Da Ros, Valentina Indio, Alberto Peloso, Claudia Tregnago, Giulia Borella, Maddalena Benetton, Giorgia Longo, Silvia Bresolin, Barbara Buldini, Andrea Pession, Franco Locatelli, Martina Pigazzi
Journal: HemaSphere (2023)

Background: Pediatric acute myeloid leukemia (AML) is a life-threatening disease with chemotherapy and hematopoietic stem cell transplantation still representing the standard of care. Nowadays, most of children affected from AML reached complete remission, but 30% experienced relapse indicating an urgent need to identify more effective therapies to treat resistance and recurrence events. In last years, genomic characterization improved the success in the identification of molecularly targeted compounds. Nevertheless, despite promising preclinical data, less than 10% of novel candidate cancer drugs have been authorized for market, failing Phase I-II of clinical trials. This latter phenomenon is mainly due to poor correlation of drug safety/efficacy in humans with respect to preclinical models. Thus, optimization of preclinical tools to advance clinically relevant data have been pursued, with patient derived xenografts (PDXs) resulting the most predictive in vivo AML models. Aims: This study aims to establish, characterize, and use pediatric AML-PDXs to accelerate the identification and evaluation of innovative medicines. Methods: We established PDXs by inoculating primary AML samples in NSG mice and, when engrafted, in consequent mice recipients (P0, P1 and P2-PDXs). We characterized AML by immunophenotipic profile, RNA-seq and whole-exome sequencing (WES). According to somatic mutations we determined AML clonal dynamics. Interrogating omics data we selected novel drugs, tested in vitro, on three-dimensional (3D) co-culture system and in vivo, on PDXs. Results: We generated 26 AML-PDXs representatives of 14 different AML genetic subtypes. Immunophenotype, genomic and transcriptomic profiles of PDXs showed strong similarity to the original AML. By WES we detected a consistent number of variants in each model (from 24 to 67) and we did not identify mutations recurrence among AML, confirming an high intra-tumoral heterogeneity. We tracked clonal evolution from patients to P2-PDXs recognizing “founder” clones characterized by an average of 25 variants (at least one in driver AML genes) maintained in P2 at similar allelic frequency (AF=50%), other small clones increasing the AF in P2 and, in a restricted number of models, patients’ clones characterized by variants in driver genes (KRAS,MYCN,SETD2) have been lost in PDXs. RNA-seq analysis unravel aberrantly expressed and druggable pathways that allowed to select novel targeted drugs (IACS-10759, Asparaginase(ASPN), Disulfiram, Gallein, Thioridazine, SNDX-5613, Trametinib). By exploiting a 3D system in vitro (a biomimetic scaffold co-cultured with blasts and mesenchymal stromal cells) we screened the efficacy of these drugs, used alone or combined with Venetoclax (VEN) to explore synergistic effects. Most efficacious combinations in 3D, VEN+IACS and VEN+ASPN (p<0.001, n=4), have been evaluated in 6 KMT2A-rearranged PDX models. Results showed that 3/6 models underwent remission after 4 weeks of treatment with VEN, whereas 6/6 models treated with combos had leukemia eradication at stop treatment. At day +15 after stop therapy, 6/6 models treated with VEN showed increased disease burden, whereas only 1 model treated with VEN+IACS, and 1 with VEN+ASPN, relapsed; 4/6 PDXs treated with the combos are still in remission at day +45. Summary/Conclusion: The generation of a large panel of AML-PDXs and relative omics data represent a concrete perspective to identify new variants/pathways involved in AML progression. Predictive drug screenings in PDXs will increase the portfolio of AML drugs with higher chance to advance in pediatric AML second line treatments. Keywords: OMICS, Mouse model, Acute myeloid leukemia, Pediatric